When obstructive sleep apnea (OSA) occurs, the reduction in blood oxygen saturation level during the apnea attack is accompanied by a rapid rise in blood pressure, and this subjects the cardiovascular system to an immense pressure load. This pressure load is a strong candidate as a mechanism responsible for cerebrovascular disease and cardiovascular events such as myocardial infarction, and the evaluation of the cardiovascular risk of a patient based on information regarding this rise in blood pressure is very important in the management of various types of disorders.
As a conventional method for estimating the cardiovascular risk of an OSA patient, Patent Literature 1 (JP 2009-66269A) proposes a method of continuously measuring the blood oxygen saturation level and finding the time integral of values below a predetermined threshold value. Also, Patent Literature 2 (JP S62-155829A) proposes a method of automatically measuring blood pressure when the blood oxygen saturation level decreases.